In electronic cameras, the light-sensitive elements or pixels convert light incident through an objective of the camera into electric signals. Each of the pixels is addressed to read out an image, with each pixel corresponding to a respective picture element of the image. The pixels arranged in rows and columns form an image field of the image sensor. A signal which is proportional to a charge of the pixel collected by an exposure is conducted to an output of the image sensor.
Image sensors are in particular known which have a separate row selection line for each row and a separate column line for each column. The reading out of such an image sensor takes place row-wise, i.e. row for row. For this purpose, the pixels of the respective row are switched to the column lines by means of the respective row selection line. A separate column amplifier is usually associated with each of the column lines. The column amplifiers are provided for the purpose of amplifying the signals of the pixels of the selected row applied to the column lines. The amplified signals are conducted to the data output via a multiplexer device or, if a plurality of data outputs are provided, as is preferred to achieve a high picture rate, to the plurality of outputs of the image sensor.
A separate data output is also not usually provided for each column line and/or each column amplifier with a plurality of data outputs since a substantial space requirements and thus cost expense is associated with every data output. For example, 32 data outputs (per channel) can be provided for an image sensor having 4096×3112 pixels. The number of data outputs is as a rule therefore smaller than the number of column lines and/or column amplifiers, i.e. a plurality of column lines and/or column amplifiers are associated with the respective data output via at least one multiplexer device. This means that the signals transmitted by the plurality of column lines are read out via the respective “associated” data output.
Provision can be made to increase the dynamic range of the image sensor that the signals of the pixels are read out by two or more mutually separate channels which amplify the signals by different amounts. In such a case, the image sensor can include e.g. 2×32 data outputs, with then the same column lines and/or column amplifiers being associated with the respective data output of the second channel as with the associated data output of the first channel. The data outputs associated with the first channel and the data outputs associated with the second channel each in particular form a group of similar data outputs with the respective same amplification.
In the aforesaid example, 128 (4096:32) column lines and/or column amplifiers which are arranged next to one another and which form a respective column line group and/or column amplifier group are thus multiplexed to a respective data output. Generally, the number of column lines per column line group corresponds to the multiplex factor of the at least one multiplexer device of the image sensor, i.e. n column lines per column line group on an n-fold multiplexing.
As a rule, the individual data outputs cannot be manufactured completely identically with one another. The properties of the data outputs, in particular output amplifiers of the data outputs and/or analog/digital converters of the data outputs, rather differ slightly from one another. For example, an offset voltage or an amplification can be slightly different for different data outputs. The picture elements associated with the respectively differing data output then appear somewhat brighter or darker in comparison with the other picture elements.
A column line group is defined in connection with the present invention in that each column line group includes a plurality of column lines arranged next to one another and the number of column lines of the column line group corresponds (at least mathematically) to the number of column lines which are associated with a respective data output of the image sensor. In other words, the number of column line groups corresponds to the number of data outputs of the image sensor, with the column lines of each column line group being arranged next to one another. There is a problem with such a division of the column lines into column line groups when all column lines of a respective column line group are associated with the same data output (and only with it). Such a division admittedly has the advantage that no horizontal buses are required which ultimately connect the outputs of the column amplifiers to the data outputs and have to extend over the total width of the image sensor (high energy consumption, large space requirement, low speed). Instead, the data outputs are locally associated with the respective column line group and horizontal connections can be correspondingly short or can be omitted. However, with such a strict division, all picture elements associated with a column line group have a slightly different brightness in the case of a difference of the aforesaid kind, i.e. a larger region of contiguous picture elements or a whole picture field block has a slightly different brightness. A block-shaped brightness difference arises. A different brightness of one or more image field blocks from the brightness of the other image field blocks can be easily perceived by the eye and has a disturbing effect on the viewer. The image sensor explained in the aforesaid example with 32 data outputs (per channel) includes, for example, 32 image field blocks disposed next to one another.